need prop advice

[jtrom]

I know this is a complex question. I have a 15 ft old aluminum runabout and a 1974 Johnson 50 HP looper motor (I heard these have low torque) that I'm gonna put on it. The boat is rated for 50 hp max and this boat is light weight compared to my old fiberglass trihull that the motor came off. What would be a good prop pitch to use in this setup?..

 

[steelespike]

Re: need prop advice

Best thing is to run it with the present prop and get the max rpm and speed.
Llikely will have to increase pitch but some al boats can be hard to push so it could require the same prop. As far as low torque it appears that the 74 and say the 88 run the same gear ratio.
also a very brief look seems to indicate all the models based on that power head have the same ratio. 2:42.1

 

[jtrom]

Re: need prop advice

I heard it has low torque because its a 2 cylinder "loop charged " engine...also the prop is so beat up I'm afraid to run it anymore. I think the old prop is a 15 pitch...I really need to replace it before I run the motor. Should I just go with a 17?